Conventional window units incorporating a sliding window or sash employ weather stripping which extends around the sash when it is closed to provide a window seal. Such weather stripping can be mounted on the frame of the sash or on the window frame in which the sash slides or on both the sash and window frame and is compressed between the sash and window frame to effect the window seal.
Manipulation of the sash on opening and closing the window subjects such weather stripping to frictional wear and tear. As a result, such exposure to frictional abrasion limits the nature of the weather stripping which can be used to solid type strips with limited compressibility or spreadability thereby limiting the effectiveness of the window seal. The effectiveness of this seal in turn decreases with the frictional wear and tear under continued usage.
U.S. Pat. No. 4,704,821, issued Nov. 10th, 1987, discloses a floating slideable lower sash attached to a complex balance arrangement which is actuated to displace the bottom edge of the sash laterally against weather stripping as it reaches the closed position. However, such special arrangement is expensive and does not provide a uniform seal around the sash by simple closing of the sash. Further, such arrangement does not positively preclude frictional wear of the weather stripping on manipulation of the sash.